The so-called remote type plasma processing apparatus is known in which processing gas is introducing between a pair of electrodes and plasmatized by glow discharge, then, this plasma flow is blown on a substance to be processed which substance is located outside the electrodes, so that surface processing of the substance is executed (For example, Japanese Patent Application Laid-Open No. H11-251304, Japanese Patent Application Laid-Open No. H09-92493, etc.). Another plasma processing apparatus is also known in which two flat plate-like electrodes are arranged in parallel (Japanese Patent Application Laid-Open No. H07-85998, Japanese Patent Application Laid-Open No. H09-92493, etc.).
In the remote type plasma processing apparatus using the elongate parallel electrode plates, an amount of surface processing equal to the length of the long-sized electrodes can be executed at a time by blowing off a plasma flow between the longitudinal side edges of the electrodes, and thus the processing speed can be enhanced. However, the electrodes are occasionally deformed, for example, in such a manner as to approach each other at intermediate parts thereof in the longitudinal direction by Coulomb's force which is caused by applied electric field (see imaginary lines of FIG. 12). This phenomenon becomes clearly seen when the length of the electrodes is, for example, 50 cm or more. The more the length is increased, the more manifest the phenomenon becomes. When such deformation occurs, the blowoff of plasma gas is increased at the opposite end parts in the longitudinal direction of the electrodes and decreased at the intermediate parts thereof. Thus, processing uniformity is failed.
Bending deformation can also occur due to difference in thermal expansion at the time of heating the electrodes with electric current. That is, normally, the internal temperature of one electrode is higher at a part thereof nearer to the other electrode and at a part thereof nearer to the back surface. This temperature difference causes a thermal expansion difference which results in bending deformation. Bending deformation also occurs due to difference in thermal expansion coefficient between the metal which constitutes the electrodes and a solid dielectric layer coated on the metal electrodes by melt-spray or the like. This again can jeopardize the processing uniformity.
In some instances, bending deformation can also occur due to blast processing at the time of coating the solid dielectric layer on the surfaces of the electrodes by melt-spray or the like, or due to difference in thermal expansion between the electrodes and the melt-spraying material. Moreover, bending deformation can also occur by heating or the like at the time of grinding the entire surface of the solid dielectric substance only excluding the coating surface as a positioning reference surface. Such deformation occurrable during the manufacturing process as just mentioned can also jeopardize the uniform flow of the plasma flow along the longitudinal direction of the electrodes. This again can result in non-uniform processing.